Integrated diode laser cooler

Abstract

A laser diode device includes: a heat sink including a main body portion and an electrically insulating layer located on the main body portion; a mounting layer located on the electrically insulating layer, wherein the mounting layer includes a first mounting pad and a second mounting pad electrically insulated from each other; a laser diode bar located on the first mounting pad; a contact bar located on the second mounting pad; a first solder layer providing an electrical connection between the contact bar and the second mounting pad; and a plurality of wire bonds providing an electrical connection from a top surface of the laser diode bar to a top surface of the contact bar.

Description

Technical Field

[0001] The present disclosure relates to integrated diode laser coolers. Background Art

[0002] High power semiconductor laser diodes are cooled to keep junction temperature and carrier leakage low and reliability high. The laser diode can be mounted on an electrically insulating cooler, which helps to reduce thermal impedance. Summary of the invention

[0003] Generally, in some aspects, the subject matter of the present disclosure can be embodied in laser diode devices, which include: a heat sink, which includes a main body portion and an electrically insulating layer located on the main body portion; a mounting layer located on the electrically insulating layer, wherein the mounting layer includes a first mounting pad and a second mounting pad electrically insulated from each other; a laser diode bar located on the first mounting pad; a contact bar located on the second mounting pad; a first solder layer, which provides an electrical connection between the contact bar and the second mounting pad; and a plurality of wire bonds, which provide an electrical connection from a top surface of the laser diode bar to a top surface of the contact bar.

[0004] Embodiments of the laser diode device may include one or more of the following features. For example, in some embodiments, the first mounting pad is separated from the second mounting pad by a gap. The width of the gap between the opposing edges of the first mounting pad and the second mounting pad may be less than about 1.5 mm. The edge of the contact bar may extend above the edge of the second mounting pad and overlap the gap. The edge of the contact bar may extend less than about 0.5 mm above the edge of the second mounting pad. The edge of the contact bar may extend entirely above the gap. The edge of the contact bar may extend above the gap and a portion of the first mounting pad. The dielectric material may fill the gap. The dielectric material may include epoxy. The distance between the opposing edges of the contact bar and the laser diode bar may be about 0.5 mm to about 1 mm. The laser diode device may include a second solder layer between the first mounting pad and the bottom surface of the laser diode bar, wherein the second solder layer provides an electrical connection between a first electrode located on the bottom surface of the laser diode bar and the first mounting pad. The top surface of the laser diode bar may include a second electrode, and a plurality of wire bonds may provide an electrical connection from the second electrode to the contact bar. Each of the plurality of wire bonds may have a length of about 5 mm to about 6 mm.

[0005] Generally, in some aspects, the subject matter of the present disclosure can be embodied in a method of manufacturing a laser diode device, wherein the method includes: providing a heat sink, wherein the heat sink includes a main body portion, an electrically insulating layer located on the main body portion, and a mounting layer located on the electrically insulating layer; modifying the mounting layer to form a first mounting pad and a second mounting pad electrically insulated from the first mounting pad; mounting a laser diode bar on the first mounting pad so that the laser diode is electrically connected to the first mounting pad; mounting a contact bar on the second mounting pad; and electrically connecting the laser diode bar to the contact bar by providing a plurality of wire bonds coupled to a top surface of the laser diode bar and a top surface of the contact bar.

[0006] Embodiments of the method may include one or more of the following features. For example, in some embodiments, modifying the mounting layer to form a first mounting pad and a second mounting pad includes stamping the mounting layer to form a gap within the mounting layer, wherein the gap defines a spacing between the first mounting pad and the second mounting pad.

[0007] Modifying the mounting layer to form the first mounting pad and the second mounting pad may include grinding or etching the mounting layer to form a gap within the mounting layer, wherein the gap defines a spacing between the first mounting pad and the second mounting pad. In some embodiments, modifying the mounting layer to form the first mounting pad and the second mounting pad includes forming a shelf or ledge on the first and / or second mounting pad using stamping, grinding, or etching.

[0008] In some embodiments, modifying the mounting layer to form a first mounting pad and a second mounting pad includes forming a gap within the mounting layer, wherein the gap defines a spacing between the first mounting pad and the second mounting pad, and wherein mounting the contact bar includes positioning the contact bar on the second mounting pad such that an edge of the contact bar extends over the gap. The method may also include filling the gap with a dielectric material.

[0009] In some embodiments, mounting the contact bar on the second mounting pad includes soldering the contact bar to the second mounting pad to electrically connect the contact bar to the second mounting pad.

[0010] In some embodiments, the methods include simultaneously soldering the contact bar to the second mounting pad and soldering the laser diode bar to the first mounting pad.

[0011] Embodiments of the subject matter disclosed herein may include one or more of the following advantages. For example, in some embodiments, electrically insulating the mounting pads from each other may eliminate the need to use adhesive plastic foil to join the electrical contact strips. Eliminating the foil may also prevent contamination that may otherwise be caused by the foil during the packaging process. In some embodiments, the apparatus and methods disclosed herein allow for a reduction in the number of packaging steps, thereby saving more time and potentially allowing automation of the packaging process.

[0012] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1A is a schematic diagram showing a top view of an example of an electrically isolated laser diode cooler having multiple mounting pads.

[0014] Figure 1B is a diagram showing the electrical insulation of the laser diode cooler through the Figure 1A Schematic diagram of a side view of section AA.

[0015] Figure 2A is a schematic diagram showing a top view of an example of a semiconductor laser diode and electrical contacts mounted to an electrically insulating laser diode cooler having a plurality of mounting pads.

[0016] Figure 2B is a diagram showing the electrical insulation of the laser diode cooler through the Figure 2A Schematic diagram of a side view of section AA.

[0017] Figure 2C is a diagram showing the electrical insulation of the laser diode cooler through the Figure 2A Schematic diagram of a side view of section BB.

[0018] Figure 3 is a schematic diagram showing a bottom view of an example of a contact strip. DETAILED DESCRIPTION

[0019] In order to maintain low junction temperature, carrier leakage and high reliability, high power semiconductor laser diodes can be cooled by mounting the laser diode to an electrically insulating cooler. An example of an electrically insulating cooler to which a laser diode can be mounted is an ILASCO diode cooler, which is made of a stack of thin copper sheets sandwiched between two ceramic-copper sheets, thereby having high thermal conductivity. Each stacked copper sheet includes an etched structure defining a coolant channel through which a coolant is provided. A conductive mounting pad is formed on the top surface of one of the ceramic sheets. The laser diode can then be mounted directly to the conductive mounting pad using solder. For example, the p-side contact of a semiconductor laser diode can be mounted directly to the conductive mounting pad. Similarly, a separate contact strip can be mounted to the conductive mounting pad. A separate contact strip can be used to provide a conductive platform to which the opposite contact (e.g., n-side contact) of the laser diode can be coupled. To prevent the contact strip from electrically shorting with the p-side contact through the mounting pad, the contact strip is mounted to the conductive mounting pad using an insulating adhesive (e.g., plastic foil). During the manufacturing process, portions of the plastic foil are peeled off the finished device, which can cause contamination of the front facet of the laser diode. If this contamination occurs, the laser diode may need to be scraped to remove the plastic. Typically, adhesive application, plastic removal, and scraping can be labor-intensive processes that are difficult to automate.

[0020] Figure 1A-1B is a schematic diagram showing an example of an electrically insulating laser diode cooler 100 that can be used in place of a diode cooler comprising a sticky plastic foil. In particular, Figure 1A is a schematic diagram showing a top view of the electrical insulation cooler 100, and Figure 1B Is the penetration of the electrical insulation cooler Figure 1A Side view of section AA.

[0021] The cooler 100 includes a heat sink formed by a body portion 102 and an electrically insulating layer 108 on the body portion 102. The body portion 102 may include, for example, internal coolant channels through which a coolant may flow to absorb heat generated by the laser diode and carry the heat away to maintain the laser diode at a constant temperature. Therefore, in order to provide high heat transfer, both the body portion 102 and the layer 108 are formed of materials having high thermal conductivity. However, in order to reduce electrical corrosion of the body portion 102, the material of the layer 108 may also have high electrical insulation properties. For example, the body portion may be formed of a metal such as copper, which has a thermal conductivity of about 385.0 W / m*K, and the electrically insulating layer 108 may be formed of aluminum nitride having a thermal conductivity of about 140 W / m*K and a resistivity greater than about 1014 ohm*cm. In some cases, the cooler 100 also includes an opening 112 in the body portion 102 and the electrically insulating layer 108. The opening 112 provides a coupling region where a coolant may be provided.

[0022] The mounting layer 105 is formed on the electrically insulating layer 108. The mounting layer 105 is formed of a material having a high electrical conductivity (e.g., a metal or a composite, such as copper, a copper-diamond composite, molybdenum, silver, or gold, etc.) to provide an electrical contact pad for the semiconductor laser diode. Compared to a laser diode cooler using a plastic adhesive foil, the mounting layer 105 includes a plurality of electrical contact mounting pads that are electrically insulated from each other. For example, the mounting layer 105 may include a first mounting pad 104 and a second mounting pad 106. In order to electrically insulate the mounting pads from each other, the mounting pads may be separated by a physical gap. For example, as Figure 1A and Figure 1B As shown, the first mounting pad 104 is physically and electrically separated from the second mounting pad 106 by a gap 110. Since the mounting pads 104, 106 are also formed on the electrically insulating layer 108, there is little conductivity between the pads through the layer 108. By electrically insulating the mounting pads from each other, the adhesive plastic foil used to adhere the electrical contact strips can be eliminated from the package design because the foil is no longer needed to provide electrical insulation.

[0023] The plurality of contact strips (e.g., pads 104, 106) may be formed by first providing a layer of conductive material (e.g., copper) on the upper surface of the electrically insulating layer 108. For example, a layer of copper may be deposited directly onto the upper surface of the electrically insulating layer 108. Standard deposition techniques such as physical vapor deposition, electron beam deposition, or electroplating may be used to form the conductive mounting layer 105. The conductive material may be formed to have a thickness in a range between about 50 nm to about tens of microns, including, for example, between about 0.5 microns to about 15 microns.

[0024] The contact pads can then be defined by forming gaps in the provided conductive material. For example, the gap 110 can be formed by performing ion milling or chemical etching on the conductive material of the mounting layer 105 only in the area where the gap 110 is to be defined. The process may include, for example, depositing a resist as a mask, and then using photolithography to define the gap area in the resist mask before performing grinding or etching. Other applicable techniques for defining the gap may be used instead. For example, in some cases, the gap 110 may be formed by stamping the conductive mounting layer 105 before bonding or mounting it to the electrically insulating layer 108. As a result of the etching process, a plurality of electrically insulating mounting pads (each having the same thickness) may be formed to be in direct contact with the surface of the electrically insulating layer 108. In some embodiments, forming the gap 110 may expose the underlying electrically insulating layer 108. The width of the gap 110 between the opposing edges of the first mounting pad 104 and the second mounting pad 106 may be less than about 1.5 mm. For example, the width of gap 110 may be approximately 1.25 mm or less, 1 mm or less, 0.75 mm or less, or 0.5 mm or less.

[0025] In some embodiments, the gaps 110 between the mounting pads are empty (e.g., only air exists in the gap between each mounting pad). In other embodiments, the gaps 110 may be filled with an electrically insulating material. For example, the gaps 110 may be filled with a dielectric, a polymer, an epoxy, or a glue, e.g., EA 3422. The gap material may be applied to fill the gap 110 using, for example, a syringe.

[0026] Figures 2A-2C is a schematic diagram showing an example of a laser diode cooler (e.g., cooler 100) after the laser diode and contact bars are mounted to mounting pads. In particular, Figure 2A is a schematic diagram showing a top view of a laser diode cooler, and Figure 2B is a diagram showing the cooler through- Figure 2A A schematic diagram of a first side view of section AA and Figure 2C is a schematic diagram showing a second side view of the through section BB of the cooler.

[0027] exist Figures 2A-2C In an example of the present invention, the laser diode 200 is mounted to the first mounting pad 104. For example, the laser diode 200 may include a first electrode (e.g., a p-type contact) on its bottom surface, which is electrically connected to the first mounting pad 104. The laser diode 200 may include, but is not limited to, an edge emitting diode, such as a GaAs edge emitting laser diode. The laser diode 200 may be physically and electrically connected to the first mounting pad 104 using a solder connection (e.g., a first solder layer between the mounting pad 104 and the laser diode 200). For example, the laser diode 200 may be soldered to the first mounting pad 104 using AuSn, AuSnBi, tin-silver-copper, silver sintering paste, gold diffusion bonding, or other solder layers.

[0028] Separately, contact bar 202 is mounted to second mounting pad 106. Contact bar 202 provides an electrical contact area to which a second electrode (e.g., an n-type contact) of the top surface of laser diode 200 can be electrically connected. Contact bar 202 can include a material having a high electrical conductivity, such as copper, a copper-diamond composite, molybdenum, silver, or gold, etc. Contact bar 202 can be physically and electrically connected to second mounting pad 106 using a solder connection (e.g., a second solder layer between mounting pad 106 and contact bar 202). For example, contact bar 202 can be soldered to second mounting pad 106 using an AuSn solder layer. Since a solder layer is used instead of a plastic adhesive foil, the problem of adhesive foil accidentally contaminating the facets of laser diode 200 can be avoided. In some embodiments, laser diode 200 and contact bar 202 can be mounted during the same step of the packaging process, thereby reducing the number of processing steps. For example, instead of mounting the laser diode 200 to the underlying mounting pads in a first step, and mounting the contact strips 202 using a plastic adhesive foil in a separate second step, both the contact strips 202 and the laser diode 200 can be mounted to their respective mounting pads simultaneously using the same reflow process. The reduction of steps can provide further time savings and potentially allow automation of the packaging process.

[0029] After mounting both the laser diode 200 and the contact bar 202, an electrical connection is made between the top electrode (e.g., n-type contact) of the laser diode and the contact bar 202. For example, the top contact of the laser diode 200 can be wire bonded to the contact bar 202 using wire bonds 204. Typically, the distance of the gap 210 between the edge of the contact bar 202 facing the laser diode 200 and the edge of the laser diode 200 facing the contact bar 202 is about 0.5 mm to about 1 mm. The length of each wire bond 204 (extending from the laser diode to the contact bar) is about 5 mm to about 6 mm.

[0030] In some embodiments, contact strip 202 includes a shelf or ledge 206. Shelf or ledge 206 can be an area of ​​contact strip 202 where the bottom surface (i.e., the surface facing the underlying mounting layer (e.g., mounting layer 105)) is not in contact with mounting layer 105. For example, Figure 2C and Figure 3 As shown, the shelf or ledge 206 of the contact strip 202 includes a region of the contact strip that is thin relative to a portion 208 of the contact strip that is soldered to the second mounting pad 106. Figure 2C The shelf or ledge 206 is formed in the manner shown, and the contact strip 202 does not physically contact the first mounting pad 104. Therefore, the shelf 206 helps to maintain the electrical insulation of the contact strip 202 and the first mounting pad 104. Figure 2CAs shown, the shelf or ledge 206 extends over the edge of the second mounting pad 106 and the gap 110. Extending the shelf or ledge 206 over the gap 110 allows the contact strip to be positioned closer to the laser diode 200 so that the wire bonds 204 can be easily formed without requiring too long a bonding length. The shelf or ledge 206 can extend less than about 2 mm beyond the edge of the second mounting pad 106 in the direction toward the laser diode 200. For example, the shelf or ledge 206 can extend beyond the edge of the second mounting pad 106 by about 1.5 mm or less, about 1.25 mm or less, about 1 mm or less, about 0.75 mm or less, about 0.5 mm or less, or about 0.25 mm or less. Thus, in some embodiments, the shelf or ledge 206 extends entirely over the gap 110 between the first mounting pad 104 and the second mounting pad 106, and in some cases, also extends over a portion of the first mounting pad 104.

[0031] Figure 3 2 is a schematic diagram showing a bottom view of the contact bar 202. The bottom view depicts the surface of the contact bar 202 facing the mounting layer 105 below. As explained herein, the shelf or ledge 206 of the contact bar 202 can correspond to an area of ​​the contact bar 202 that is thinner than the area of ​​the contact bar 202 that is directly mounted on the mounting pad below. The shelf or ledge 206 can be formed by removing a portion of the contact bar. For example, the shelf or ledge 206 can be formed by grinding or etching the contact bar 202. The remaining portion 208 of the contact bar 202 that is not removed can then be bonded to the mounting pad below (e.g., the second mounting pad 106) using a solder layer. The edge of the shelf or ledge 206 that faces the laser diode 200 can have a width 212. The width 212 can be substantially the same as the width of the edge of the laser diode that the shelf 206 faces to allow wire bonds to be formed across the width of the laser diode. For example, in some embodiments, the width 212 can range from about 1 mm to about 20 mm.

[0032] In some embodiments, an electrically insulating material may be formed in the space between the shelf or ledge 206 of the contact strip 202 and the upper surface of the mounting layer 105. The electrically insulating material may include a dielectric, a polymer, an epoxy, or a glue, for example, EA 3422. The gap material may be applied using, for example, a syringe to fill gap 110. The electrically insulating material filling the space between shelf or ledge 206 and mounting layer 105 may provide additional bonding force to hold contact strip 202 in place. In some embodiments, the electrically insulating material may ensure that shelf 206 does not make electrical contact with first mounting pad 104.

[0033] Other aspects, advantages, and modifications are within the scope of the following claims.

Claims

1. A laser diode device, comprising: a heat sink comprising a main body portion and an electrical insulation layer located on the main body portion; a mounting layer on the electrically insulating layer, wherein the mounting layer includes a first mounting pad and a second mounting pad electrically insulated from each other by a gap; a laser diode bar located on said first mounting pad; a contact bar on the second mounting pad, the contact bar comprising a contact portion and a ledge, the contact portion being soldered to the second mounting pad, the bottom surface of the ledge not contacting the mounting layer, wherein the ledge extends over the gap to allow the contact bar to be positioned closer to the laser diode bar, and the ledge comprises a region having a thickness thinner than a thickness of the contact portion; a first solder layer providing an electrical connection between the contact bar and the second mounting pad; and A plurality of wire bonds provide electrical connections from a top surface of the laser diode bar to a top surface of the ledge.

2. The laser diode device according to claim 1, wherein: The first mounting pad is spaced apart from the second mounting pad by a gap.

3. The laser diode device according to claim 2, wherein: The width of the gap between the opposing edges of the first mounting pad and the second mounting pad is less than 1.5 mm.

4. The laser diode device according to claim 2, wherein: The contact strip has an edge that extends over an edge of the second mounting pad and overlaps the gap.

5. The laser diode device according to claim 4, wherein: The edge of the contact strip extends less than 0.5 mm above an edge of the second mounting pad.

6. The laser diode device according to claim 2, wherein: The contact strip has an edge extending entirely over the gap.

7. The laser diode device according to claim 2, wherein: The contact strip has an edge extending over the gap and over a portion of the first mounting pad.

8. The laser diode device according to claim 2, wherein: A dielectric material fills the gap.

9. The laser diode device according to claim 8, wherein: The dielectric material includes epoxy resin.

10. The laser diode device according to claim 2, wherein: The distance between the contact bar and the opposite edge of the laser diode bar is 0.5 mm to 1 mm.

11. The laser diode device according to claim 2, wherein: The laser diode device includes a second solder layer between the first mounting pad and the bottom surface of the laser diode bar, wherein the second solder layer provides an electrical connection between a first electrode on the bottom surface of the laser diode bar and the first mounting pad.

12. The laser diode device according to claim 10, wherein: The top surface of the laser diode bar includes a second electrode, and the plurality of wire bonds provide electrical connections from the second electrode to the ledge.

13. The laser diode device according to claim 2, wherein: Each of the plurality of wire bonds has a length of 5 mm to 6 mm.

14. A method of manufacturing a laser diode device, the method comprising: Providing a heat sink, wherein the heat sink comprises a main body portion, an electrical insulation layer located on the main body portion, and a mounting layer located on the electrical insulation layer; modifying the mounting layer to form a first mounting pad and a second mounting pad electrically insulated from the first mounting pad by a gap; mounting a laser diode bar on the first mounting pad such that the laser diode is electrically connected to the first mounting pad; mounting a contact bar on the second mounting pad, the contact bar comprising a contact portion and a ledge, the contact portion being soldered to the second mounting pad, the bottom surface of the ledge not contacting the mounting layer, wherein the ledge extends over the gap to allow the contact bar to be positioned closer to the laser diode bar, and the ledge comprises a region having a thickness thinner than a thickness of the contact portion; The laser diode bar is electrically connected to the contact bar by providing a plurality of wire bonds coupled to a top surface of the laser diode bar and a top surface of the ledge.

15. The method of manufacturing a laser diode device according to claim 14, wherein: Modifying the mounting layer to form the first mounting pad and the second mounting pad includes stamping the mounting layer to form a gap within the mounting layer, wherein the gap defines a spacing between the first mounting pad and the second mounting pad.

16. The method of manufacturing a laser diode device according to claim 14, wherein: Modifying the mounting layer to form the first mounting pad and the second mounting pad includes grinding or etching the mounting layer to form a gap within the mounting layer, wherein the gap defines a spacing between the first mounting pad and the second mounting pad.

17. The method of manufacturing a laser diode device according to claim 14, wherein: modifying the mounting layer to form the first mounting pad and the second mounting pad includes forming a gap within the mounting layer, wherein the gap defines a spacing between the first mounting pad and the second mounting pad, and Wherein, mounting the contact bar comprises positioning the contact bar on the second mounting pad so that an edge of the contact bar extends above the gap.

18. The method of manufacturing a laser diode device according to claim 17, wherein: The method includes filling the gap with a dielectric material.

19. The method of manufacturing a laser diode device according to claim 14, wherein: Mounting the contact bar on the second mounting pad includes soldering the contact bar to the second mounting pad to electrically connect the contact bar to the second mounting pad.

20. The method of manufacturing a laser diode device according to claim 14, wherein: The method includes simultaneously soldering the contact bar to the second mounting pad and soldering the laser diode bar to the first mounting pad.

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